Introduction to C
Programming
Hong Liu
HPC Consultant
NICS
• A Brief History of C
• In 1972 C was first wrote at Bell Labs.
• In 1978 the publication of The C Programming
Language caused a revolution in the computing
world.
• In 1983, the American National Standards Institute
(ANSI) established a committee to provide a
modern, comprehensive definition of C. The
resulting definition, the ANSI standard, or "ANSI
C", was completed late 1988.
• Why C?
Features of C language Uses of C language:
Reliability
Portability
Flexibility
Interactivity
Modularity
Database systems
Graphics packages
Word processors
Spread sheets
Operating system development
Compilers and Assemblers
Network drivers
Interpreters
Running C Programs
Developing a program in a compiled language such as C requires
at least four steps:
• editing (or writing) the program *.c
• compiling it *.obj
• linking it
*.exe
(stdio.h)
• executing it
Using Microsoft C
• Edit stage:
• Type program in using one of the Microsoft Windows editing
packages.
• Compile and link:
• Select Build from menu. Building option allows you to both
compile and link in the same option.
• Execute:
• Select the Build menu → then, Execute filename.exe menu
Unix systems
• Online terminal emulator
• http://simpleshell.com/
• hello world example
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#include <stdio.h>
main()
{
printf("Hello world\n");
}
• Please note that Unix is a case sensitive operating system and
files named firstprog.c and FIRSTPROG.c are treated as two
separate files on these system.
• By default the Unix system compiles and links a program in
one step, as follows: cc firstprog.c
• This command creates an executable file called a.out .
• The program is run as follows:
• ./a.out
Add Comments to a Program
• A comment is a note to yourself (or others). All
comments are ignored by the compiler.
• /* This is a comment. */
• main() /* main function*/
•{
• printf("Hello, World! \n"); /* DisplayMessage */
•}
Data Types
• You can create variables to store values in. There are
five basic data types associated with variables:
• int - integer: a whole number.
• float - floating point value: ie a number with a
fractional part.
• double - a double-precision floating point value.
• char - a single character.
• void - valueless.
• An int variable can store a value in the range -32768
to +32767. No fractional part is allowed.
• To declare an int : int variable name;
• int a ; Declares that you want to create an int
variable called a.
• To assign a value to our integer variable we would
use the following C statement:
• a=10;
• Decimal Number Variables: float and double.
• float: A float number has about seven digits of
precision and a range of about 1.E-36 to 1.E+36.
• double: A double number has about 13 digits of
precision and a range of about 1.E-303 to
1.E+303.
• To declare : float total; double sum;
• Assign a numerical value to our floating point
and double precision variables:
• total=0.0; sum=12.50;
• Character Variables
• To declare a variable of type character we
use the keyword char.
• For example:
• char c;
• To assign, or store, a character value in a
char :
• c='A'
void
• Basically it means "nothing" or "no type"
• In C if you don’t specify the return type, the
compiler automatically inferred that you wanted
to return an int
• Function return value: void myFunc(int) -the function returns nothing
True and False in C
• In C true is represented by any numeric value not
equal to 0 and false is represented by 0.
• if(a)
• If a isn't zero then this also acts as the value true
Mathematical operations
Add, subtract, multiply and divide.
• add a+b
• subtract a-b
• multiply a*b
• divide a/b
• What is the answer to this simple
calculation?
• a=10/3
• The answer depends upon how a was
declared. If it was declared as type int the
answer will be 3; if a is of type float then
the answer will be 3.333.
• #include <stdio.h>
• main(){
• int a,b,average;
• a=10; b=6;
• average = ( a+b ) / 2 ;
• printf("Here is the answers.. ");
• printf("\n");
• printf("%d.",average);
• printf("\n");
• }
Input and Output Functions
• Input functions, called scanf
• scanf("%d",&a);
• Output functions, called printf
• printf("The value stored in a is %d",a);
• #include <stdio.h>
• main()
• {
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• }
int a,b,c;
printf("\n The first number is ");
scanf("%d",&a);
printf("The second number is ");
scanf("%d",&b);
c=a+b;
printf("The answer is %d \n",c);
• #include <stdio.h>
• main()
•{
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•
•
}
int dec = 5;
char ch = 's';
float pi = 3.14;
printf("%d %f %c\n", dec, pi, ch);
Functions
A function has the general form:
type FunctionName (type declared parameter list)
{
statements that make up the function
}
#include<stdio.h>
void demo()
{
printf("Hello");
}
main()
{
demo();
}
Making The Connections
• How to get data into a function? parameters are used
to carry data values into a function. Parameters are
listed and declared in between the () brackets in the
function's definition
• sum( int a, int b){
• int result;
• result=a + b;
•}
• sum(l,2);
• How do we get values out?
• return value;
• int sum(int a, int b){
• int result;
• result = a + b;
• return result;
• }
• And to use it you can write something like:
• r=sum(1,2);
• void demo();
• is a function with no parameters and no return value.
• #include<stdio.h>
int sum(int a, int b){
int result;
result=a+b;
return result;
}
main(){
int r;
r=sum(1,3);
printf("The answer is %d.\n", r);
}
The Standard Library
Functions
• stdio.h: I/O functions:
• printf() as previously described
• scanf() as previously described
• string.h: String functions
• strcpy() copys contents of str2 to str1
• ctype.h: Character functions
• islower() returns non-0 if arg is lowercase letter
• isupper() returns non-0 if arg is uppercase letter
• math.h: Mathematics functions
• sqrt() returns square root of num
• time.h: Time and Date functions
• time() returns current calender time of system
Data Types Part II
• So far we have looked at local variable now we switch our
attention to other types of variables supported by the C
programming language:
• Global variables
• int max;
• main(){
• .....
• }
• f1(){
• .....
• }
• Constant Data Types
• Fixed values that may not be altered by program
• #define CONSTANTNAME value
• For example:
• #define SALESTAX 0.05
• #define SALESTAX 0.05
• #include <stdio.h>
• main() {
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• }
float amount, taxes, total;
printf("Enter the amount purchased : ");
scanf("%f",&amount);
taxes = SALESTAX*amount;
printf("The sales tax is £%4.2f",taxes);
printf("\n The total bill is £%5.2f",total);
Questions?